1. Field of the Invention
This invention relates to a lost motion correction system and a lost motion correction method for a numerical control machine tool. This invention further relates to a lost motion correction value setting method for a machine tool of a hybrid control system, a computer readable recording medium for recording a program for executing this method on a computer, and a numerical control machine tool.
2. Description of Relevant Art
The numerical control machine tool includes a holding and processing portion for holding and processing a workpiece in a space defined by imaginary axes, and a numerical controller for providing electrical control commands for causing the holding and processing portion to make necessary actions. The numerical control machine tool has drives by axes that mechanically act in dependence on the control commands, and a group of mechanical elements that transmit mechanical actions of the drives to the holding and processing portion. A transmission system for mechanically transmitting the control commands to a position for the workpiece to be held and/or processed is constituted by the mechanical element group and mechanical elements of the drives and the holding and processing portion.
The numerical controller calculates reverse functions of transmission functions by axes of the transmission system, with respect to necessary actions of the holding and processing portion, to thereby obtain the control commands.
However, mechanical elements of the transmission system are respectively real rigid bodies and, when operated, have engagement slips at their meshing engagement parts or frictional engagement parts, deformations by elongation and deflection depending on acting forces, and thermal deformations depending on their temperatures. Amounts of such slips and deformations have their components by axes, of which integrations along the transmission system give values that represent errors between the control commands and real actions of the holding and processing portion.
Among the errors, such an error that occurs due to a directional difference in motion of the holding and processing portion, or more specifically, a positioning error occurring between a positioning to an identical target point in a positive sense (at an advance side) and that in a negative sense (at a return side) is called a lost motion error.
The lost motion error is caused by a backlash due to loose engagement in and a windup due to deflection of mechanical elements. It has delicate variations depending on acting conditions of respective elements, and is difficult to be estimated by calculations.
In the past, therefore, the numerical control machine tool was operated for a trial run, where lost motion errors were measured as detail as possible and lost motion correction values for canceling them were parametrically set, and control commands for actual processing were corrected by the set correction values to thereby effect a lost motion correction.
For example, in Japanese Patent Application Laid-Open Publication No. 8-263117, there has been proposed measuring lost motion errors at a plurality of processing positions for each of a plurality of feed speeds, and respectively setting corresponding lost motion correction values.
For this reason, in the past, in adjustment at the maker end factory of a numerical control machine tool or in installation at the user end factory, there was employed a high-precision measurement machine such as a laser measurement machine, so that machine positions were actually measured by a maker side engineer taking a long time, and then a careful trial run was repeated for measurement of lost motion errors.
It therefore was difficult to perform, at the user end alone, resetting lost motion correction values in accordance with a condition of use of the numerical control machine tool.
This invention was made with the above-noted point in view. It is an object of this invention to provide a lost motion correction method and a lost motion correction system for a numerical control machine tool that allows a necessary precision for processing to be kept by measuring lost motion errors with their dynamical properties in view, even with a moderated measuring precision.
It also is an object of this invention to provide a lost motion correction value setting method for a machine tool of a semi-close/full-close hybrid loop control system, in which lost motion errors can be measured without employing a measuring machine of a particularly high precision, and lost motion correction values can be set at the user end alone, as well as a computer readable recording medium for recording a program for executing this method on a computer, and a numerical control machine tool.
To achieve the object, according to a first aspect of the invention, there is provided a lost motion correction method for a numerical control machine tool for correcting a lost motion error of a mechanical transmission system including a first mechanical element to be operated in accordance with a control command from a control program and a second mechanical element for positioning a control object to target positions. This lost motion correction method comprises detecting an operated amount of the first mechanical element, detecting an operated position of the second mechanical element, recognizing from the control program that the control object stops at a first target position, calculating a stationary lost motion error as a lost motion error along a motion stop of the mechanical transmission system upon a positioning of the control object to the first target position, based on the operated amount of the first mechanical element and the operated position of the second mechanical position, setting a first lost motion correction value for canceling the stationary lost motion error, and correcting, by the first lost motion correction value, a first control command for positioning the control object to the first target position.
According to a second aspect of the invention, a lost motion correction method according to the first aspect further comprises recognizing from the control program that the control object changes a moving direction at a second target position, calculating a dynamic lost motion error as a lost motion error along a continuous motion of the mechanical transmission system upon a positioning of the control object to the second target position, based on the operated amount of the first mechanical element and the operated position of the second mechanical position, setting a second lost motion correction value for canceling the dynamic lost motion error, and correcting, by the second lost motion correction value, a second control command for positioning the control object to the second target position.
Further, to achieve the object described, according to a third aspect of the invention, there is provided a lost motion correction system for a numerical control machine tool for correcting a lost motion error of a mechanical transmission system including a first mechanical element to be operated in accordance with a control command from a control program and a second mechanical element for positioning a control object to target positions. This lost motion correction system comprises a first detector configured to detect an operated amount of the first mechanical element, a second detector configured to detect an operated position of the second mechanical element, a recognizer configured to recognize from the control program that the control object stops at a first target position, a calculator configured to calculate a stationary lost motion error as a lost motion error along a motion stop of the mechanical transmission system upon a positioning of the control object to the first target position, based on the operated amount of the first mechanical element and the operated position of the second mechanical position, a setter configured to set a first lost motion correction value for canceling the stationary lost motion error, and a corrector configured to correct, by the first lost motion correction value, a first control command for positioning the control object to the first target position.
According to a fourth aspect of the invention, in a lost motion correction system according to the third aspect, the recognizer is configured to recognize from the control program that the control object changes a moving direction at a second target position, the calculator is configured to calculate a dynamic lost motion error as a lost motion error along a continuous motion of the mechanical transmission system upon a positioning of the control object to the second target position, based on the operated amount of the first mechanical element and the operated position of the second mechanical position, the setter is configured to set a second lost motion correction value for canceling the dynamic lost motion error, and the corrector is configured to correct, by the second lost motion correction value, a second control command for positioning the control object to the second target position.
Further, to achieve the object described, according to a fifth aspect of the invention, there is provided a lost motion correction value setting method for a numerical control machine tool of a hybrid control system for performing a positional loop control by using machine position signals output from a position detecting scale for detecting a machine position and motor position signals output from a rotary encoder for detecting a rotation angle of a driving servo motor. This lost motion correction value setting method comprises executing a test program to periodically input the machine position signals and the motor position signals, calculating differences between the machine position signals and the motor position signals to determine errors, calculating a difference between an average value on an advance side and an average value on a return side of the errors, and holding the difference as a dynamic lost motion correction value.
According to a sixth aspect of the invention, in a lost motion correction value setting method according to the fifth aspect, an arc interpolation or a linear reciprocal axis control is performed by the test program, and the lost motion correction value is calculated to be held for each feed axis.
According to a seventh aspect of the invention, in a lost motion correction value setting method according to the fifth or sixth aspect, Xi is defined as a coordinate of a target position to be designated at an i-th time with respect to an arbitrary coordinate axis X by the test program, and a decision of the advance side and the return side is automatically made in a manner in which a coordinate Xi-1 is deemed as a reverse position when three coordinates Xi, Xi-1, and Xi-2 to be contiguously designated meet a condition of (Xixe2x88x92Xi-1) (Xi-1xe2x88x92Xi-2) less than 0.
Further, to achieve the object described, according to an eighth aspect of the invention, there is provided a lost motion correction value setting method for a numerical control machine tool of a hybrid control system for performing a positional loop control by using machine position signals output from a position detecting scale for detecting a machine position and motor position signals output from a rotary encoder for detecting a rotation angle of a driving servo motor. This lost motion correction value setting method comprises executing a test program to perform a reciprocal pitch feed, inputting the machine position signals obtained at respective stop positions on an advance side and at respective stop positions on a return side of identical command positions, and storing an average value of differences therebetween as a stationary lost motion correction value.
According to a ninth aspect of the invention, there is provided a computer readable recording medium for recording a program for executing on a computer a lost motion correction value setting method according to any of the fifth to eighth aspect.
According to a tenth aspect of the invention, there is provided a numerical control machine tool of a hybrid control system having a computerized numerical controller for executing a lost motion correction value setting method according any of the fifth to eighth aspect.